Prosecute to restrict member that's lying (6)
'lying' is the definition.
'prosecute to restrict member' is the wordplay.
'prosecute' becomes 'sue' (I've seen this before).
'to restrict' indicates putting letters inside.
'member' becomes 'pin' (pin is a kind of member**).
'sue' going around 'pin' is 'SUPINE'.
'that's' acts as a link.
(Other definitions for supine that I've seen before include "Recumbent", "Flat on one's back", "Laid-back", "Slow in acting", "Inert; on one's back".)